The price of soda drinks and pizza affects their level of consumption and therefore has an effect on health outcomes, a 20 year US study has concluded. It suggests that imposing a tax on junk food might improve the nation’s health.

The coronary artery risk developments in young adults (CARDIA) study is notable for its scope, duration, and measurement of both physiological and economic factors. Beginning in 1985 it recruited a broadly representative sample of 5115 adults aged 18 to 30 in four cities in the United States (Archives of Internal Medicine 2010;170:420-6).

The researchers periodically measured participants’ height, weight, insulin resistance, and other clinical factors, …